There is known, as one of output devices of computers and workstations, an image forming apparatus employing an ink-jet system in which ink is ejected to form an image on a recording medium. The image forming apparatus employing an ink-jet system comprises, for example, a print head for ejecting ink, a carriage on which the print head is mounted, said carriage reciprocating in a predetermined direction, a recording medium conveying device for conveying recording mediums in a direction intersecting perpendicularly to the predetermined direction, and a print plate disposed at a position in which the print plate is opposite to the print head reciprocating, wherein a recording medium is conveyed on one side (a surface facing the print head) of the print plate.
In recording of an image on a recording medium, the recording medium being conveyed by the recording medium conveying apparatus (device) is once stopped. A fraction of the image is formed in a long and narrow band shape by ejection of ink from a reciprocatingly moving print head in accordance with image signals on the recording medium in an image formation area. Then the recording medium is moved forward by the breadth of the formed fractional image, and is stopped to form another image fraction on an adjacent unprinted portion of the recording medium. Such operation is repeated to form the entire image on the recording medium.
As the above-mentioned recording medium conveying apparatus, there is known such a type of one having, for example, a first conveyance roller for supporting and conveying a recording medium, and a second conveyance roller for supporting and conveying the recording medium discharged from the first conveyance roller, which are disposed on the upward stream side and the downward stream side with respect to a direction of the recording medium conveyance across the print plate from one another, respectively.
In such a type of recording medium-conveying apparatus, if the sheet-shaped recording medium curls after passage through the first conveyance roller, the front end portion of the recording medium is directed upward or downward, and cannot be caught and conveyed by the second conveyance roller. Therefore, the recording medium may not be exactly conveyed, or may be hooked by surrounding parts to cause jamming of the recording medium.
An area put between the first conveyance roller and the second conveyance roller forms the image formation area for an image formation. Consequently, in order to obtain a good quality of image, there is a need to convey recording mediums in the flat state free from the above-mentioned trouble.
Usually, as a technology of conveying recording mediums in the flat state, there is known a guide plate system wherein a guide plate, which extends in a direction intersecting perpendicularly to the recording medium conveying direction, is disposed between the first conveyance roller and the second conveyance roller, and is fixed in such a manner that the inlet side of the recording medium is opened and the outlet side of the recording medium is narrowed, so that the recording medium is guided through the guide plate. As alternative technology, there are known a suction system wherein a suction fan is disposed below the print plate to convey a recording medium to the second conveyance roller while the recording medium is sucked, and an electrostatic system wherein a recording medium is conveyed while the recording medium is absorbed on an electrostatic basis.
By the way, in the image forming apparatus employing an ink-jet system, in order to obtain a good quality of image, there is a need to make the print head come close to the recording medium. For this reason, usually, there is no space around the print plate. According to the above-mentioned guide plate system, the guide plate is disposed between the first conveyance roller and the second conveyance roller, and this keeps the print head away from the first conveyance roller or the second conveyance roller. Therefore, it is hard to ensure the flatness of the portion facing the print head, of the recording medium, and thus there is a possibility such that the quality of image is degraded. In addition, this is associated with such a problem that the tip margin of the recording medium becomes large unnecessarily. Further, for the image forming apparatus employing an ink-jet system, there is a need, at the time of image formation, to cope with a cockling (a phenomenon in which a recording medium partially absorbing ink expands and whereby unevenness is formed on the expanded portion and its periphery) which will occur on the recording medium. Thus, also in this respect, the guide plate system is disadvantageous.
On the other hand, according to the suction system as mentioned above, the suction fan is disposed below the print plate. This needs the space for such an arrangement. Thus, the suction system is disadvantageous from a viewpoint of miniaturization of the apparatus and low cost of the apparatus. Further, also with respect to the electrostatic system, in a similar fashion to that of the suction system, it is disadvantageous in miniaturization of the apparatus and low cost of the apparatus.